A hero's welcome given by Libya to former intelligence agent sparked anger on Friday in the United States and Britain which both warned Tripoli of serious diplomatic repercussions. The former officer was convicted in 2001 of taking part in the bombing on Dec 21, 1988 of a passenger plane, and sentenced to life in prison.

The airliner exploded over Scotland and all 259 people aboard and 11 on the ground died when it crashed into the town of Lockerbie in Scotland.

Hundreds of people waving Libyan and Scottish flags greeted Abdelbaset Ali Mohmed al-Megrahi as he landed in Tripoli late on Thursday. According to AFP, Megrahi said he was 'very relieved' to be freed but described his conviction as a 'disgrace'. Megrahi returned with an official delegation who included Libyan leader Moamer Kadhafi's son Seif al-Islam.

The scenes of jubilation came despite a call by the United States that it would be monitoring reactions carefully. President Barack Obama said he believed the Scottish government had blundered in approving his release. "We're now in contact with the Libyan government and want to make sure that ... that he's not welcomed back in some way, but instead, should be under house arrest," said Obama.

On his part, State Department spokesman PJ Crowley said it had been made very clear to Libya that "he is not entitled to a hero's welcome."